Hybrid vehicles generally consist of an electric traction motor, or motors, that drive the vehicle wheels, storage batteries to supply electrical energy to the traction motor, and some sort of generator/alternator driven by an internal combustion engine (ICE) to charge the batteries and/or provide the power for the traction motor. In a series hybrid vehicle, there is no mechanical connection between the drive wheels and the ICE. The ICE is used only to drive the alternator/generator. The engine/alternator combination provides a means of converting the chemical energy of the fuel to electrical energy.
This invention is directed specifically to a series hybrid type of vehicle having a regenerative braking system in which the drive motor is converted to a generator that provides a large and often excessive output of useful electrical energy. More particularly, it is directed to a construction for recovering the useful energy that is normally wasted if, for example, the storage battery is already fully charged.
In a hybrid vehicle, start-up of the ICE is independent of the initial drive-away of the vehicle since the ICE does not power the wheels of the vehicle. When this is possible, the conditions under which engine start-up occurs can be optimized. It is well documented that nearly 80% of a conventional ICE-powered automobile's emissions are generated during cold start-up and drive-away, as mentioned above. An engine maintained at some elevated temperature, optimally 125.degree. F. to 180.degree. F., for example, could be started without the need for fuel enrichment, i.e., air/fuel ratios richer than stoichiometric (chemically correct air/F ratio), resulting in significantly improved exhaust emissions.
The invention provides a unique energy recovery system for the regenerative braking system of the hybrid vehicle. It utilizes a control system that allows the traction motor to function as a generator during braking to absorb the vehicle's kinetic energy that normally would be dissipated and lost by conventional brakes. The kinetic energy is converted to electrical energy that can recharge the storage batteries, provide heat to the ICE coolant and other components of the ICE, or be stored for future use in a heat battery type storage device.
In general, in a hybrid vehicle equipped with regenerative braking, a normal use scenario would be that the operator would recharge the vehicle every night to ensure maximum battery energy for the following day's usage. A fully charged battery, however, precludes utilization of regenerative braking and the associated recoverable energy until the battery has been somewhat depleted and allows room to accept the energy from the regenerative braking.
This invention is directed specifically to a system for recovering the electrical energy developed during regenerative braking that is in excess of that necessary to charge the vehicle's storage battery, so that the energy is not wasted. In this particular case, the excess energy is used to heat the ICE coolant to prewarm the engine when it is inoperative and the coolant is below a predetermined temperature level, and also to provide heat to the vehicle passenger car compartment heater, and to store excess heat in a heat battery for future use.
The system would perform a dual function in that it would act as an "energy reservoir" as well as allow regenerative braking to function at all times. Normally, in a conventional installation, the regenerative braking must be shut off if the storage battery cannot use it. This system eliminates that disadvantage since the energy reservoir can be tapped to, as stated, preheat the engine for low emission start-ups, heat the passenger compartment, or be stored in a heat battery for future use.
The invention, therefore, is directed specifically to the utilization of the electrical energy generated during regenerative braking of the hybrid vehicle so that the regenerative braking need not be shut off.